The present invention relates to a connecting structure and connecting method for electric cables, in which two electric cables made of heterogeneous metals are connected to each other so as to have a waterproof function.
Copper electric cables are widely used as electric cables for supplying power to houses or for the wiring of electronic devices, since copper electric cables have high electric conductivity, high rigidity relative to gold electric cables or aluminum electric cables and advantages in terms of mechanical strength and price. On the other hand, aluminum electric cables using aluminum or aluminum alloy as a conductor material are desirable when considering demand for the lightweight of vehicles, large amount of resource that ensures stable supply, recyclability that facilitates separation from steel, and the like.
Due to such desires, these days, such aluminum electric cables are widely used as electric cables for vehicles. Such an aluminum electric cable is electrically connected to a circuit device or the like through a terminal that is connected to a distal end of the aluminum electric cable. The terminal is made of copper or copper alloy having spring force by which the terminal can be in tight contact with a counterpart terminal. Since contact corrosion may be undesirably caused by contact of heterogeneous metals, when the aluminum electric cable is used, various measures for corrosion resistance are carried out for the terminal to be connected to the aluminum electric cable.
As for the electric cables for vehicles, the connection reliability between a copper electric cable and a terminal is ensured based on a performance evaluation including an endurance test and data that has been accumulated during actual driving. However, when the aluminum electric cable instead of the copper electric cable is connected to the terminal as described above, massive amounts of time and cost are consumed because the optimization of press-contact conditions, the verification of connection reliability, the optimization of a terminal structure, and the like must be performed.
Therefore, there is a technology for connecting the aluminum electric cable to the terminal made of copper or copper alloy without performing the optimization of press-contact conditions, the verification of connection reliability, the optimization of a terminal structure, and the like. A related-art connecting structure for electric cables, that prevents the contact corrosion in the connection portion between the terminal and the aluminum electric cable is presented by, for example, Patent Document 1. In the related-art connecting structure, by connecting a short copper electric cable between the terminal and the aluminum electric cable, it is possible to avoid the connection between heterogeneous metals in the terminal to prevent contact corrosion.
As shown in FIG. 7, in the related-art connecting structure for electric cables, one end of a conductor 34 of a short copper electric cable 36 which is formed by covering the conductor 34 made of copper or copper alloy with an insulator 35 is connected to a conductor terminal of an aluminum electric cable 33 which is formed by covering a conductor 31 made of aluminum or aluminum alloy with an insulator 32, and the connected portion is covered with an insulator 37. In addition, in the related-art connecting structure for electric cables, a terminal 38 made of copper or copper alloy is connected to the other end of the conductor 34 of the copper electric cable 36 by press-contact connection.
According to the related-art connecting structure, since the copper electric cable 36 is press-contacted to the terminal 38 made of copper or copper alloy, there is no danger that contact corrosion due to the contact of heterogeneous metals might occur in an electric cable press-contact section. In addition, in the electric cable press-contact section, it is possible to ensure high connection reliability by utilizing the performance evaluation and the result of the actual use of terminals that have been cultivated to date. Along with this, in the terminal press-contact section, it is possible to reduce massive amount of time and cost that is consumed for the optimization of press-contact conditions, the verification of connection reliability, the optimization of terminal structure, and the like. In addition, since the connection portion between the aluminum electric cable 33 and the copper electric cable 36 is covered with the insulator 37, it is possible to prevent water, vapor or the like from entering into the connection portion from the outside, thereby suppressing the foregoing occurrence of contact corrosion between heterogeneous metals.
Patent Document 1: Japanese Patent Application Publication No. 2009-009736
The connecting structure for electric cables according to the related art has the following problems to be solved.
Since the terminal or the short copper electric cable connected to the terminal is not waterproof, when an engine room of a vehicle or the like is cleaned in the state in which the connection portion is not sufficiently covered with an insulator, for example, a drop of water attached to the aluminum electric cable may permeate to a terminal in the electronic circuit side or to the electronic circuit through the connection portion between the aluminum electric cable and the copper electric cable due to a capillary phenomenon, and is attached to the connection portion between the aluminum electric cable and the copper electric cable, thereby causing the foregoing contact corrosion between heterogeneous metals to occur. In particular, when the copper electric cable or the aluminum electric cable is a strand produced by twisting or braiding a plurality of cores together, a drop of water, which permeated into a gap between the cores of the aluminum and copper electric cables or between the cores and the insulating cover, accelerates contact corrosion in the connection portion.